Let me ask you about usocket and force-output.
I made a simple Echo server to study usocket. It's echo1 and echo2. I tried telnet connection to echo1 and it worked fine. However, when I tried to telnet to echo2, I sent a string to the server, but the server didn't respond.
(defunecho1 (host port)
(usocket: with-socket-listener (socket host port)
(do() (nil nil)
(usocket: with-server-socket(usocket: socket-accept socket:element-type'(unsigned-byte8))))
(let((stream(usocket:socket-stream socket)))
(do(byte (read-byte stream nil)
(read-byte stream nil)))
((null byte)nil)
(write-byte byte stream)
(force-output stream)))
(defun echo2 (host port)
(usocket: with-socket-listener (socket host port)
(do() (nil nil)
(usocket: with-server-socket(usocket: socket-accept socket:element-type'(unsigned-byte8))))
(let((stream(usocket:socket-stream socket)))
(do(byte (read-byte stream nil)
(read-byte stream nil)))
((null byte)nil)
(write-byte byte stream))
(force-output stream)))
The difference between echo1 and echo2 is, of course, the force-output position. So, I asked, why is this difference caused by the difference in the position of force-output?In addition, our processing system is SBCL.
common-lisp socket
This is because input data is buffered until force-output is executed.
force the output to be written to the network?
When you write output to the stream, it may be buffered before sent over the network-for optimum performance of small writes. You can force the buffer to be flushed the same way as with normal streams:
(format(socket-stream socket) "Hello there~%"; output into buffers
(force-output (socket-stream socket);;<==flush the buffers, if any
echo1 sends it to the client side socket line by line, but echo2 buffers it until EOF is entered (not sent to the client side).
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